1. Technical Field
The present invention relates to, for example, an electro-optical device such as LCD, etc., particularly, an electro-optical device and an electronic apparatus having the same adopting a reversal driving system in which the polarity reversal of a driving voltage is regularly implemented for each pixel line or pixel row so that voltages of pixel electrodes adjacent to each other in a line direction or row direction of a pixel show a reverse polarity to each other.
2. Related Art
In this kind of electro-optical device, there is adopted the reversal driving system in which the voltage polarity applied to each pixel electrode is reversed in accordance with a predetermined rule for the prevention of a deterioration of an electro-optical material and a crosstalk or a flicker on a display image caused by the application of D.C. voltage.
During the display corresponding to an image signal of one frame or field out of them is implemented, as the reversal driving system which enables relatively easy controlling and high-definition image displaying is used 1 H reversal driving system in which the pixel electrode arranged in even line is driven by the negative voltage potential as a voltage potential of the opposite voltage and the pixel electrode arranged in odd line is driven by the positive voltage potential as a voltage potential of the opposite electrode, while during a display corresponding to an image signal of the subsequent frame or field is implemented, the pixel electrode arranged in odd line is driven by the negative voltage potential and the pixel electrode arranged in even line is driven by the positive voltage potential (the relevant voltage polarity is reversed in a frame or field cycle for each row when the pixel electrode in the same line is driven by the voltage potential of the same polarity). In addition, as the reversal driving system which enables relatively easy controlling and high-definition image displaying is also used 1 S reversal driving system in which the relevant voltage polarity is reversed in a frame or field cycle for each row when the pixel electrode in the same line is driven by the voltage potential of the same polarity. Furthermore, there has been also developed the dot reversal driving system in which the voltage polarity applied to each pixel electrode is reversed between the pixel electrodes adjacent to the line direction and row direction.
This kind of electro-optical device is generally driven in an active matrix by mounting a holding capacitor electrically connected to a TFT and the pixel electrode. This holding capacitor holds the voltage potential applied to the pixel electrode during a fixed period, whereby the voltage potential holding characteristic can be remarkably improved in each pixel. Such holding capacitor often includes a double-layer dielectric film inserted between a pair of electrodes for the sake of securing the capacitor.
In JP-A-2003-347543 is disclosed the technology that reduces the current leakage when low electric field is applied by constituting a silicon nitride film utilized for a part of a nonvolatile memory such as a flash memory which is a type of various semiconductor devices by the layers with different composition ratio of nitrogen and silicon.
However, in case that this kind of electro-optical device is driven in the reversal driving system, the voltage applied to the holding capacitor is not applied to the opposite electrode at uniform polarity constantly, but the voltage of different polarity is applied in correspondence with the reversal driving. More specifically, the voltage potential of one dielectric film out of two dielectric films the holding capacitor has increases or decreases for the other dielectric film. That is, the direction of the electric field on two dielectric films is reversed.
As described above, although the holding capacitor has the strong voltage tolerance to one direction on two dielectric films in case that the direction of the electric field is temporarily reversed, a respectable amount of current leakage occurs in the holding capacitor during the actual use in case that the electric field of reverse direction is applied in correspondence with the reversal driving, whereby there is the technical problem that the direction dependence turns up in the voltage tolerance. The inventor thinks that one factor of the occurrence of current leakage and lowering of voltage tolerance depends on the conventional structure, the film characteristic or the segregation state of various materials on the interface state of the dielectric film that even if the holding capacitor includes two dielectric films, but it is difficult to take a proper action by grasping the cause of the occurrence of current leakage and lowering of voltage tolerance.
Moreover, from the viewpoint of the reduction of current leakage and the securing of capacitor, it is thought that the number of stack layers the holding capacitor has increases, but it is difficult to optimize the electro-optical device individually and concretely in response to the element characteristic that requires the construction of dielectric film or the condition of stack layer so that the current leakage has no effect on the actual use.
In addition, since in JP-A-2003-347543 is disclosed the only technology that reduces the current leakage by differentiating the composition ratio of two silicon nitride films, it is hard to say that more general unit for reducing the current leakage is suggested in respect to the dielectric film and stack layer structure formed by different materials.